The present invention relates to a veneer lathe having a knife for cutting a log into a veneer sheet and at least one second knife which is located on rake face side of the veneer cutting knife and adapted to form a cut or slit in the periphery of the log while embedding a cord in the slit.
Various veneer lathes of the type described have heretofore been proposed in connection with Japanese Patent Publication No. 35-4246 entitled "Improvement in Method of Preventing Damage to Veneer Sheet in Plywood Production", Japanese Patent Publication No. 39-14994 entitled "Apparatus for Reinforcement of Veneer Sheet", Japanese Patent Publication No. 49-6642 entitled "Apparatus Associated with Rotary Veneer Lathe for Burying Cord in Trimmed Edge of Log", Japanese Patent Publication No. 49-35052 entitled "Veneer Sheet Processing Method", etc. All of these known types of veneer lathes with cord embedding knives have failed, however, to achieve a systematic combination of the cord embedding knife and the veneer lathe alloted with different functions: the cord embedding knife serving to embed a cord in a log and the veneer lathe serving to cut a veneer sheet from a log.
A typical example of a prior art veneer lathe having a cord embedding knife is illustrated in FIG. 1. The cord embedding knife denoted by the reference numeral 4 is so constructed and arranged to form a cut or slit in the periphery of a turning log 2 while embedding a string or cord 3 in the slit. The log 2 reinforced by the cord 3 is cut into a veneer sheet 1 by a usual veneer cutting knife 6 which is rigidly mounted on a tool rest 7 of the veneer lathe. FIG. 2 is an enlarged sectional side view of the veneer sheet 1 turned from the cord embedded log 2. It will be observed in FIG. 2 that the cord 3 in the slit 5 of the veneer sheet 1 has locally lifted itself away from the bottom of the slit.
This undesirable phenomenon is attributable to a tension which will be discussed with reference also to FIG. 3. When the veneer sheet 1 is cut from the log 2 by the knife 6, it moves outward away from the log at a high speed and at an angle to the log which corresponds to the angle of the cutting edge of the knife 6. This results in an abrupt and intense force which pulls the cord 3 so that the cord 3 is displaced from its normal position A to an abnormal position B rising from the bottom of the slit 5. Such a displacement of the cord 3 will also be invited by any other condition which would exert a pulling force on the veneer sheet 1 during travel of the veneer sheet out of the veneer lathe. Particularly, the pulling force or tension acts in a concentrated manner on the cord 3 every time a defective portion of the veneer sheet is moved past the veneer cutting knife 6. For this reason, the cord 3 rises away from the bottom of the slit at those portions of the veneer sheet which define the rear edges of the defects with respect to the moving direction of the veneer sheet as illustrated in FIG. 2, in which the defects are represented by a lost portion 8 caused by a crack and a lost portion 9 caused by a peripheral recessed part of the log. Naturally, a loose portion of the veneer sheet, if not completely lost, brings about a similar tension exerted in a concentrated manner on part of the cord bridging the defect 8 or 9 mentioned. In this way, the conventional veneer lathe with a cord embedding knife prevents the cord from reinforcing those portions of a veneer sheet which need reinforcement most acutely, due to its very characteristics. This constitutes a critical problem in the practical use of the veneer lathe. To solve this problem, the invention disclosed in Japanese Patent Application Post-Examination Publication No. 51-31559 introduced a veneer lathe in which a similar cord embedding knife works on a veneer sheet immediately after being cut from the log to ensure that the cord buried in a cut formed in the veneer sheet will not be subjected to any external force as observed at the moment of separation from the log. However, this prior art creates another problem; that is, since the veneer sheet cut off from the log is limp and has a lot of cracks formed at the time of cutting operation, it easily buckles when worked on by the cord embedding knife and the cracks in the sheet prevent the continuous forming of an elongated cut therein.